(1) Field of the Invention
This invention relates to a device for binding a stack of sheets; and in one aspect to a device for binding a stack of paper sheets.
(2) Description of the Prior Art
The art is replete with inexpensive devices for binding stacks of sheets comprising a binding strip (support member) and a plurality of filaments adapted to engage and bind the sheets to the binding strip. Generally, however, such devices are not as efficient or convenient as may be desired.
For example, U.S. Pat. No. 3,874,705 describes a binding device having polymeric studs or monofilaments adapted to pass through apertures in a stack of paper sheets and mate with countersunk holes in a binding strip. The ends of the plastic studs or monofilaments are formed into heads within the countersink and lock the stud and binding strip together. Such a binding device requires rather complex installation equipment to cut the studs off at an appropriate length and then form the heads within the countersink by the application of heat and/or pressure.
U.S. Pat. Nos. 3,026,876; 3,176,363; and 3,217,372 describe the use of flexible, resilient, polymeric monofilaments with binding strips in loose-leaf notebooks. The filaments are threaded through apertures in paper sheets to be secured in the notebook, are bent at right angles adjacent the top sheet and secured in that position under hooks or tabs that project from the binding strip. The ends of these monofilaments are not secured against longitudinal movement, however, and thus could tend to loosen with usage of the bound document. Also the projecting hooks or tabs may not provide as smooth a profile for the binding device as may be desired for many applications.
U.S. Pat. No. 3,654,668, and Australian Pat. No. 1,196,243 describe binding devices using elongated, elastic, longitudinally extensible elements that mate with recessed locking channels in a binding strip to secure objects thereto. The binding strip of U.S. Pat. No. 3,654,668 has a channel whose diameter is less than the diameter of the unstretched element. The element is stretched to decrease its diameter during insertion into the channel, after which the element is allowed to retract toward its original dimension so that it provides an interference fit with the channel. U.S. Pat. No. 1,196,243 describes a loose-leaf paper binder using an extensible tubular element that is mated with a recessed locking channel having directly opposed teeth, which teeth exert a clamping force on the tubular element when it is placed in the channel. Binding devices using elastic, longitudinally extensible elements, however, cannot form a tight, firm binding such as is desirable for many documents.